The knee joint is one of the most important and strongest joints in the human body. It is designed to support the weight of a person's body and to provide articulating motion between the upper leg and the lower leg. Referring to FIG. 11, human knee joint 10 provides a hinged connection between the femur bone 102 of the upper leg and the tibia 104 and fibular 106 bones of the lower leg. The bone anatomy of the knee joint also includes the patella bone 108 located in the center of the knee. The distal end of the femur bone 102 includes two convex epicondyles, i.e., lateral epicondyle 126 and medial epicondyle 127 that interface and articulate with two corresponding condyles formed at the proximal end of the tibia bone 104, i.e., lateral condyle and medial condyle, respectively. The end surfaces of the condyles and epicondyles are covered by the articular cartilage 124 and between the femur and the tibia there is a plate of cartilage known as the meniscus 122. The knee joint bones are held together by a series of ligaments including the medial collateral ligament (MCL) 110, the lateral collateral ligament (LCL) 112, the anterior cruciate ligament (ACL) 114, the posterior cruciate ligament (PCL) 116, the patella tendon 118 and the quadriceps tendon 120. The MCL connects the medial site of the femur to the tibia. The LCL connects the lateral site of the femur to the fibula. The ACL extends obliquely from and connects the inner surface of the lateral epicondyle of the femur to the anterior condyle of the tibia. The PCL extends obliquely from and connects the inner surface of the medial epicondyle of the femur to the posterior condyle of the tibia. The patella bone is held in place in the anterior surface of the knee by the patellar tendon and the quadriceps tendon. The overall range of motion of the knee depends upon the specific anatomy of the bones and the ligaments and in general it allows about 120° degrees of flexion motion. In addition to the knee bones and ligaments, there is a joint capsule and small pockets of synovial fluids (i.e., bursae) that surround the knee and provide strength and lubrication. The ligaments and the fluid capsule and bursae are referred to as the soft tissue of the knee joint.
The specific anatomy of the knee bones and ligaments evolves and develops during maturation of animals and humans. Ligament migration under the evolving demands of loading and weight bearing during early stages of development has been reported by numerous researchers. Wei et al., in a study analyzing the morphological changes and insertion migration in medial collateral ligaments (MCL) states: “during development, the MCL maintains its relative position to the knee joint system despite growth at the tibial epiphyses.” Wei et al., goes on to say: “it may be speculated that increased mechanical loading on the periosteum mediated by the attaching ligament may stimulate periosteal cells to differentiate into osteoclasts by mechanisms mentioned above.” Dörfl informs us that: “If bone is inspected at different ages, one sees that the insertions of muscles and ligaments on the diaphysis occupy the same relative positions with respect to the extremities of the bone. This observation can only be explained by the migration of the insertions on the diaphysis, for it is known that there is no interstitial growth of the diaphysis.” Thomopoulos et al., describes the morphogenesis of tendon to bone insertion and identifies several mechanobiological mechanisms and factors which mitigate ligament insertion site development and migration. Wang et al., states: “The most curious of the migratory sites is the MCL, as it is an inelastic fibrous ligament that during linear growth seems to be under heavy and continuous tension from its origin on the distal femur yet manages to migrate away from rather than toward the direction of the applied load.”
It is clear that during the developmental phase, the ligament structure adapts to the developing bony structure and perhaps the osseous structures adapt and are shaped by the developing ligament structure as a result of the imposed mechanical loading. This synergistic growth process maintains the needed joint mobility while providing the requisite joint stability necessary for a functional knee system throughout the development phase and into maturity.
An anatomical and functional knowledge of ligament insertion sites is necessary to the understanding of the mechanics of the knee. Much recent research focuses on accurate anatomical studies necessary to help guide the surgeon in ligament reconstructive surgery and total knee replacement. Many of these studies focus on quantification of the ligament insertion site geometry and neighboring osseous landmarks. These studies are undoubtedly excellent references for surgeons attempting to navigate in the obscure surgical environment. However, most of these studies, even the most quantitative, omit description of the mechanical context which might be provided by measurement of the geometry of the articular surfaces. Typically we find detailed anatomical descriptions of the ligament insertion sites, accompanied by reference measurements to proximate osseous landmarks. Most frequently the osseous landmarks are of surgical interest because they are palpable or possibly visible in the near vicinity of the ligament structure of interest. But generally these landmarks are not mechanical, or if they are, their function is secondary to the principle function of the joint or perhaps structural in nature.
The shape of the contiguous articular surfaces constitutes a constraint system which guides or constrains the permissible kinematics of the joint (assuming no interpenetration which is not strictly true under load). The articular contact geometry, coupled with the geometry of the ligament structure, functions synergistically to realize the requisite stability and conversely, mobility of the joint. Thus to remove description of the ligaments from the context of description of the articular surfaces provides a mechanically incomplete description of the joint.
In total knee arthroplasty (TKA) and in knee ligament reconstruction surgery, accurate positioning of the implants and accurate ligament attachment are crucial to the success of the operations. A large percentage of these operations fail and need to be repeated because it is difficult to determine the accurate positioning of the implant and the accurate ligament attachment from purely anatomical data.
One system for obtaining data indicative of a location of a ligament graft placement in ligament reconstruction surgery is described in US published application US 20100234770. This prior art system includes a position determining device that is capable of tracking relative movement of two bones using reference bodies that are attached to the bones and a pointer that has a tip for contacting a surface of at least one of the two bones in order to capture one or more reference points. The system also includes a computer that is configured to determine and track intraoperative positions of the reference bodies and the pointer and to provide isometric and impingement data for the ligament graft placement based on realistic simulation of a trajectory of a deformable ligament graft. The system generates and compares preoperative and postoperative plots that represent knee laxity as a function of flexion. However, in many cases the preoperative state of the knee and the surrounding soft tissue is already compromised and therefore trying to replicate the preoperative state of the knee joint may be not desirable.
Accordingly, there is a need for a method for simulating ligament insertion and attachment in knee surgeries that provides accurate ligament insertion and attachment without relying in the preoperative state of the knee joint.